Researchers have shown that sea urchins have no eyes but see with their entire body. Photoreceptors seem to be located on the tip and base of the tube feet that are found all over the sea urchin's body, and are used to move. The researchers argue that the entire adult sea urchin can act as a huge compound eye, and that the shadow that is cast by the animal's opaque skeleton over the light-sensitive cells can give it directional vision.